Wednesday, July 25, 2012

LROC: 'Bulls-Eye' or Volcanic Vent?

A circular depression (700 m diameter) sits atop of a circular mound 3.7
km in diameter. It is either a perfectly placed impact crater on the
hill's summit, or a volcanic vent. Mosaic of LROC Narrow Angle Camera
(NAC) observations M181173832L & R,
LRO orbit 11,814, June 22, 2012; native resolution 1.5 meters per
pixel. View the cropped field of view (1000 px) framed and released as
the LROC Featured Image, July 27, 2012, HERE [NASA/GSFC/Arizona State University].

The fact that the crater is centered on the summit, the symmetry of the topography and the presence of a crater on the east side that appears to have dark ejecta suggest the feature might be a volcanic cone. The hill stands about 250 m above the surrounding plains and has a slope of about 8°. The slope is steeper than expected for a low basaltic shield, more consistent with a cinder cone.

The grouping of hills seen in the WAC mosaic was originally mapped as Fra Mauro Formation (basin ejecta) and crater rim material by Hackmann (1966). Looking around the area south of Autolycus, there are several hills that have craters near their summit or are symmetric in shape, both attributes that might suggest a volcanic origin. Elsewhere on the Moon, there are fields of volcanic vents that look similar to these. This may be a volcanic complex that has not yet been recognized.

An out of the ordinary view looking east by southeast over the 132 kilometers of Palus Putredinis from the subject (crater or vent) detailed in the LROC Featured Image released July 25, 2012 and the landing zone and area along Hadley Rille explored by the Apollo 15 expedition in 1971. LROC Global 100 meter mosaic over LOLA elevation model using NASA's ILIADS LMMP application [NASA/GSFC/LMMP/Arizona State University].